Hangzhou: US President Barack Obama on Saturday urged China to abide by its obligations under an international treaty in its activities in the South China Sea. He made the comments during a "candid exchange" with his Chinese counterpart, Xi Jinping, here in China before the G20 summit, the BBC quoted the White House as saying. In July, an international tribunal ruled against Chinese claims to rights in the South China Sea. China dismissed the ruling and said it would not be bound by it. The ruling was made by an arbitration tribunal under the United Nations Convention on the Law of the Sea (UNCLOS), which both China and the country that brought the case -- the Philippines -- have signed. The White House said Obama emphasised "the importance for China, as a signatory to UNCLOS, to abide by its obligations under that treaty, which the United States views as critical to maintaining the rules-based international order". China claims almost all of the South China Sea, including reefs and islands also claimed by other nations, and has caused dismay in the region by building artificial islands and restricting access. Earlier on Saturday, the US and China -- together responsible for 40 per cent of the world's carbon emissions -- formally joined the Paris global climate agreement. "History will judge today's effort as pivotal," Obama said. In December, 2015, countries agreed to cut emissions in an attempt to keep the global average rise in temperatures below two degrees.